The urticating larvae of pine processionary moth were already mentioned in treaties by Ancient Greeks and Romans but their gregarious behavior has only been detailed during the eighteenth century, leading to call them “processionaires”. Because they are major pine pests in the Mediterranean range, and moreover presently expanding northwards and upwards with climate change, the knowledge on their biology largely progressed during the following centuries but no synthetic work has ever been published. Combining entomology, ecology, genetics, mathematical modelling, medical and veterinary science, and pest management in a multidisciplinary approach, this book presents our current knowledge on Thaumetopoea processionary moths.